1. Field of the Invention
The present invention is generally in the field of electronic circuits and systems. More specifically, the present invention is in the field of communications circuits and systems.
2. Background Art
Mixer circuits are typically used in receiving systems to, for example, down-convert an input radio frequency (RF) signal prior to filtering and amplification. Receiving systems can utilize a mixer circuit in conjunction with a local oscillator to down-convert an input RF signal, which may include both desired and undesired signal components. In conventional low-IF receiving systems, the output of the mixer circuit is typically fed into a separate high pass filter, to achieve blocking cancellation of the undesired signal component at around DC level. Frequently, the desired signal extracted in this way requires amplification, which may then be provided by a low noise amplifier (LNA).
Conventional implementations of mixer circuits utilizing separate circuits to mix and filter a desired signal component introduce several drawbacks. One drawback is that reliance on separate circuits to achieve down-conversion and filtering results in a bulky solution. Another drawback is that where the undesired component of the down-converted input RF signal has substantially greater amplitude than the desired signal component, as may often be the case, the linearity requirement for the high pass filter can be stringent, making that system component particularly costly. Moreover, use of a separate high pass filter may introduce an additional noise component to the filtered output, as a result of the high pass filter's intrinsic filter noise. Subsequent amplification of the desired signal component includes amplification of the filter noise as well, thereby degrading signal quality.
Thus, there is a need in the art for a mixer circuit having a compact, cost effective implementation, and capable of providing blocking cancellation of a strong undesired signal component at around DC level after down-conversion while adding substantially no filter noise.